Nb Species Research Articles

Ultra-efficient Ru and Nb Co-Modified CeO2 Catalysts for Catalytic Oxidation of 1,2-Dichloroethane.

The oxidation of chlorinated volatile organic compounds on CeO2 is hindered by its high susceptibility to chlorine poisoning, resulting in a reduced efficiency and stability. In this study, Ru- and Nb-co-modified CeO2 catalysts were designed to achieve excellent activity, stability, and CO2 selectivity in the catalytic oxidation of 1,2-dichloroethane (EDC). The formation of Nb-O-Ce bonds was observed to enhance the surface acidic sites, thereby improving HCl selectivity and reducing the production of chlorinated byproducts. Meanwhile, it inhibits the formation of Ru-O-Ce and promotes the generation of highly dispersed RuO2 particles on the surface, enhancing the redox properties and mobility of the surface oxygen, thus increasing CO2 selectivity. In situ diffuse reflectance infrared Fourier transform spectroscopy results revealed that chlorine species preferentially attach to Nb species rather than to oxygen vacancies on the Ru/Nb/CeO2 catalyst. This allows more alkane groups to oxidize to formate on the oxygen vacancies, reducing byproduct concentration. Additionally, the oxidation of alkane groups to carboxylic acids is initiated on the Nb species, completing a comprehensive oxidation process under the synergistic effect of RuO2.

Acidity and stability of Nb(V) active sites doped in SBA-15 and ZrSBA-15: A DFT study

Mesoporous silicas are of great interest in heterogeneous catalysis due to the structural characteristics of their pores and the adjustable catalytic properties that arise from incorporating heteroatoms. The substitution of Zr and Nb into SBA-15 introduces active sites into the material, rendering it a potential catalyst for acid catalysis reactions. However, discussions regarding the acid properties and metal-support interactions in amorphous silicas functionalized with metals are limited in computational chemistry. This study aims to determine the acid strength and charge transfer effects between Zr(IV) and Nb(V) species in mesoporous silica by proposing a representative SBA-15 cluster of type 5–6. Density Functional Theory (DFT) simulations were conducted using the B3LYP/6-31G(d,p)/def2TZVP levels. The model successfully replicated trends from larger clusters, demonstrating that the more grafted onto the silica structure (i.e. have more Si-O-M bonds), the greater the acid strength of the active site. Additionally, it was found that ZrSBA-15 structures are more stable than NbSBA-15 and possess higher acid strength, a trend supported by experimental observations. The results also suggest that Nb(V) species are more effectively stabilized in ZrSBA-15 than SBA-15, likely due to the presence of Zr(IV) centers in ZrSBA-15. This research contribute to a better understanding of how the support affects the stabilization of active phases, paving the way for the rational design of silica-based heterogeneous catalysts.

Synergistic effect of Cerium and Niobium enhances the low-temperature NH3-SCR activity of Fe-containing solid waste

To develop environment-friendly low temperature NH3-SCR catalyst and realize the resource utilization of industrial solid waste, this research prepared a series NH3-SCR catalysts by using Fe-containing solid waste loading CeO2 and Nb2O5. It was found that the Ce2Nb1/Fe-Si catalyst exhibited the highest NH3-SCR activity, reaching about 93 % NOx conversion and 99 % N2 selectivity at 300 °C due to the synergistic effect between Ce and Nb species. The characterization results showed that the interaction between Ce and Nb was stronger than that between Nb and Fe species, promoting the NH3 adsorption and redox cycle of Ce4+ + Nb4+ ↔ Ce3+ + Nb5+, Ce3+ + Fe3+ ↔ Fe2+ + Ce4+, which increased the contents of Fe2+ and surface adsorbed oxygen. Moreover, the co-existence of Ce and Nb species would increase the NOx adsorption ability and promote the oxidation of NO to NO2, which was beneficial for “Fast SCR” reaction. Finally, the introduction of CeO2 and Nb2O5 did not changed the reaction mechanism, followed by a Langmuir-Hinshelwood mechanism.

Flotation performance and adsorption mechanism of α-hydroxyoctyl phosphinic acid to pyrochlore

The flotation performance and adsorption mechanism of α-hydroxyoctyl phosphinic acid (HPA) on pyrochlore were investigated through micro-flotation experiments, zeta-potential tests, contact angle measurements and XPS analysis. The flotation results demonstrated that, in comparison to N-hexadecylpropane-1,3-diamine (NHDA), HPA exhibited a comparable collecting ability for pyrochlore but displayed superior selectivity against feldspar and quartz. Adsorption experiments revealed that the pyrochlore exhibited a higher adsorption capacity for HPA compared to feldspar and quartz. The contact angle experiments indicated that the treatment with HPA significantly increased the contact angle for pyrochlore and calcite, while only minimal changes were observed for feldspar and quartz. Zeta potential and XPS data provided evidence for the chemical adsorption of HPA onto pyrochlore surfaces. Detailed XPS results showed that P-OH groups in HPA formed P(III)-O-M (M = Ca and Nb) bonds with Ca and Nb species on the pyrochlore surface. Additionally, the P-H bond in the HPA molecule could undergo a Redox reaction with highly oxidized Nb, resulting in the formation of a P(V)-Nb(IV) bond. This P(V)-Nb(IV) bond enhances the adsorption of hydrophobic HPA onto the mineral, making it easier to recover pyrochlore through flotation.

Influence of Doping of Niobium Oxide on the Catalytic Activity of Pt/Al2O3 for CO Oxidation

Pt-based alumina catalysts doped with varying niobium contents (i.e., 0, 1.20, 2.84, and 4.73 wt%, denoted as Pt/Nb–Al2O3) were synthesized via stepwise impregnation for catalytic CO oxidation. The effective incorporation of Nb species without altering the fundamental properties of the Al2O3 support was confirmed by the characterization using XRD, Raman, and TEM. Pt metallic particles were uniformly deposited on the niobium-doped alumina (Nb–Al2O3) support. H2-TPR and CO–TPD analyses were performed to reveal the influence of niobium doping on catalyst reduction and CO adsorption properties. The results consistently demonstrate that the doping of niobium affects reducibility and alleviates the competitive adsorption between CO and O2 during the CO reaction. Particularly, when compared to both undoped and excessively doped Pt/Al2O3 catalysts, the catalyst featuring a 2.84 wt% Nb content on Pt1.4/Nb2.8–Al2O3 displayed the most promising catalytic performance, with a turnover frequency of 3.12 s−1 at 180 °C. This superior performance can be attributed to electron transfer at the Pt/NbOx interface.

High-electrophilic (SiO)2Nb(OH)(=O) sites confined in silanol defects over Nb-Beta zeolite for efficient cyclic alkene epoxidation reactions

Dealuminated Beta zeolite has a large amount of silanol defects on its interface, which provides an ideal place for embedding metal species and creating metal active sites in a confined microenvironment. The confined metal sites as well as their surroundings are closely related to the reactant activation and transient state achievement. Hence, unraveling the confined metal sites is of great significance for the catalytic reaction process. Herein, niobium species were incorporated into the silanol defects over dealuminated Beta zeolite with a facile dry impregnation method, co-grinding the niobium precursor with dealuminated Beta zeolite support. The successful incorporation of niobium into the silanol defects for 30Nb-Beta zeolite was verified by DRIFT, 1H MAS NMR, UV–Vis and UV-Raman characterizations. XAS characterization and DFT calculations further disclosed that the confined Nb species existed as (SiO)2Nb(OH)(=O), containing two Si−O−Nb bonds, one Nb=O bond as well as one Nb−OH bond. The synthesized 30Nb-Beta zeolite catalyst displayed a superior cyclohexene conversion of 51.1%, cyclohexene oxide selectivity of 83.1% as well as TOF value of 188.2 h−1 ascribed to the inherent electrophilicity of Nb(V) for confined (SiO)2Nb(OH)(=O) species as well as the low oxygen transfer energy barrier for NbV−OOH species. Furthermore, the prepared 30Nb-Beta zeolite can be effectively employed to other cyclic alkene epoxidation reactions.

Niobium Modification of CeO2 Tuning Electron Density of Nickel-Ceria Interfacial Sites for Enhanced CO2 Methanation.

CO2 methanation has attracted considerable attention as a promising strategy for recycling CO2 and generating valuable methane. This study presents a niobium-doped CeO2-supported Ni catalyst (Ni/NbCe), which demonstrates remarkable performance in terms of CO2 conversion and CH4 selectivity, even when operating at a low temperature of 250 °C. Structural analysis reveals the incorporation of Nb species into the CeO2 lattice, resulting in the formation of a Nb-Ce-O solid solution. Compared with the Ni/CeO2 catalyst, this solid solution demonstrates an improved spatial distribution. To comprehend the impact of the Nb-Ce-O solid solution on refining the electronic properties of the Ni-Ce interfacial sites, facilitating H2 activation, and accelerating the hydrogenation of CO2* into HCOO*, in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) analysis and density functional theory (DFT) calculations were conducted. These investigations shed light on the mechanism through which the activity of CO2 methanation is enhanced, which differs from the commonly observed CO* pathway triggered by oxygen vacancies (OV). Consequently, this study provides a comprehensive understanding of the intricate interplay between the electronic properties of the catalyst's active sites and the reaction pathway in CO2 methanation over Ni-based catalysts.

Solvent‐Free Selective Oxidation of Benzyl Alcohol at Atmospheric Pressure Catalyzed by Pd Nanoparticles Supported on g‐C3N4 Materials with Tunable Nitrogen Distributions

AbstractSolvent‐free atmospheric selective oxidation of benzyl alcohol (BZA) by molecular oxygen is a promising and green process for the synthesis of benzaldehyde (BZL). Supported Pd nanoparticles have been widely reported in the catalytic selective oxidation of BZA where the activity depends on the chemical valence and dispersion of the Pd nanoparticles. Herein, a series of thermally exfoliated g‐C3N4 (eg‐C3N4) have been synthesized under various gas conditions (air/N2) and then applied as catalyst supports to load Pd nanoparticles. The physicochemical properties of the prepared Pd/eg‐C3N4 materials have been characterized by N2 adsorption–desorption, XRD, FT‐IR, UV‐vis, XPS, and TEM. Pd nanoparticles dispersed well on the supports, and the distributions of Pd and nitrogen species of the catalysts were related to the gas conditions of the supports. In the selective oxidation of BZA, 2.5Pd/eg‐C3N4‐AN catalyst afforded conversion of BZA and the selectivity to BZL of 88 % and 92 %, respectively. The metallic Pd0 species are considered the catalytic sites of Pd/eg‐C3N4 in the catalytic reaction and meanwhile, the basic Nb species of eg‐C3N4 were beneficial to the overall activity of the catalyst.

The Facile Microwave-Assisted Coprecipitation Route to Obtain Polyoxoniobate (Na7(H3O)Nb6O19·14H2O) Nanorods Modified with Copper for CO2 Photoreduction

The CO2 reduction by solar means has been discussed as an alternative to emission abatement, a fundamental topic for sustainable, carbon-free production in the future. However, the choice of efficient systems, starting with the catalysts, is still a critical issue, especially due to the poor activity of available options. Polyoxometalates have been extensively studied as promising photocatalysts due to their semiconducting properties. Nevertheless, the synthetic conditions of polyoxoniobate are stringent due to the low reaction activity of Nb species, the lack of soluble precursors, and the narrow pH range. Unlike the literature, in the present study, we report a simple polyoxoniobate synthesis method. This synthesis method has some remarkable features, such as low processing time and temperature and good activity and selectivity in the CO2 photoreduction process. The results revealed an outstanding efficiency for the CO2 reduction reaction with a high selectivity of CO2 to CO conversion (92.5%). Furthermore, C2 compounds (e.g., acetate) were produced in the liquid phase of the reaction system. Our findings are significant for indicating the potential of polyoxoniobate for CO2 photoreduction, which opens a way to control competitive reactions with synthesis, leading to higher selectivity.

Investigation on the mechanism of Nb and Si co-doping on low SO3 generation from V-based catalyst during NH3-SCR process

Generally, SO3 tends to be formed in the process of selective catalytic reduction (SCR), and SO3 has negative effects on atmospheric environmental production and the safe operation of coal-fired power plants. In this study, a series of Nb and Si codoped V-based catalysts were prepared via the impregnation method, and Nb and Si species were applied to reduce the SO3 generation ratio from the catalyst. Moreover, the controlled condensation method was used to collect the SO3, which formed during the NH3-SCR reaction process. The results indicated that the Nb and Si codoped catalysts exhibited the best NO reduction performance with the lowest SO3 generation ratio. The SO3 generation ratio and the NO conversion ratio for the VW2NbTi-10Si catalyst were 0.39% and 92%, respectively. The physicochemical properties of the catalysts were analysed by a series of characterization techniques. The X-ray diffraction (XRD) results revealed that the Nb and Si species could inhibit the crystallization of TiO2, and the X-ray photoelectron spectroscopy (XPS) results indicated that Nb and Si could decrease the ratio of Oα and V5+ on the surface of the catalyst. From the CO2 and NH3 temperature programmed desorption (CO2 and NH3-TPD) results, the Nb and Si species could reduce the number of alkaline sites on the catalyst surface, and the Si species could significantly enhance the acidity of weak and strong acid sites over the catalyst. Combined with the results of N2-adsorption and desorption, CO2-TPD, H2 temperature programmed reduction (H2-TPR) and XPS experiments, the addition of Nb and Si species was beneficial to inhibiting the adsorption and oxidation of SO2 on the surface of catalysts, resulting in a significant decrease in SO3 emissions. Therefore, in-situ diffuse reflective infrared Fourier transform spectroscopy (DRIFTS) analysis demonstrated that the Nb and Si species could restrict the reaction between SO2 and V species, decreasing the formation of the intermediate product VOSO4. Furthermore, the enhancement of reaction temperature and NH3 volumetric fraction would significantly promote the formation of SO3. However, the variations in the volumetric fraction of O2 and NO expressed ignorable effects on the SO3 generation ratio.

Effects of impregnation sequence on the NH3-SCR activity and hydrothermal stability of a Ce-Nb/SnO2 catalyst

Hydrothermal stability is crucial for the practical application of deNOx catalyst on diesel vehicles, for the selective catalytic reduction of NOx with NH3 (NH3-SCR). SnO2-based materials possess superior hydrothermal stability, which is attractive for the development of NH3-SCR catalyst. In this work, a series of Ce-Nb/SnO2 catalysts, with Ce and Nb loading on SnO2 support, were prepared by impregnation method. It was found that, the NH3-SCR activities and hydrothermal stabilities of the Ce-Nb/SnO2 catalysts significantly varied with the impregnation sequences, and the Ce-Nb(f)/SnO2 catalyst that firstly impregnated Nb and then impregnated Ce exhibited the best performance. The characterization results revealed that Ce-Nb(f)/SnO2 possessed appropriate acidity and redox capability. Furthermore, the strong synergistic effect between Nb and Sn species stabilized the structure and maintained the dispersion of acid sites. This study may provide a new understanding for the effect of impregnation sequence on activity and hydrothermal stability and a new environmental-friendly NH3-SCR catalyst with potential applications for NOx removal from diesel and hydrogen-fueled engines.

Modelling microstructure formation in TiAl by isomorphic inoculation

Ti-Al alloys have replaced Ni-based superalloys in the last stages of some aircraft engines to improve fuel efficiency. In order to improve their properties, grain refinement has been investigated via isomorphic inoculation with Ti-Al-Nb particles. This inoculation method is orders of magnitude more efficient on a particle-by-particle basis than traditional inoculation, rather than multiple inoculant particles added to form a solidified bulk phase grain, in isomorphic inoculation each particle added results in the formation of multiple grains. As the particles are indistinguishable from the matrix after solidification, a model was used to elucidate this mechanism. Two phenomena were considered to calculate the number of particles acting during solidification: particle breakup along grain boundaries and complete particle dissolution. The grain size of the particles was calculated with an empirical model from initial TKD analysis of the particles and high temperature molten salt heat treatments. Particle dissolution was estimated via mass transport of the slowest diffusing Nb species. This showed the population of isomorphic inoculant particles which can act during solidification is near a 1:1 ratio with the number of grains formed, confirming the mechanism of grain refinement by direct epitaxial growth from the particles.

Atmospheric and Efficient Selective Oxidation of Ethylbenzene Catalyzed by Cobalt Oxides Supported on Mesoporous Carbon Nitride

Mesoporous carbon nitride (mpg-C3N4) was prepared by using cyanamide as a precursor and colloidal nanosilica as a template. Then, the mpg-C3N4 was used as a catalytic support to load CoOx. The physicochemical properties of the synthesized CoOx/mpg-C3N4 materials were elucidated by multiple characterization methods, and the catalytic activities were examined in the selective oxidation of ethylbenzene (EB) under atmospheric pressure by using tert-butyl hydrogen peroxide (TBHP) as an oxidant. It was found that mpg-C3N4 possessed a higher specific surface area than other carbon nitride materials, and its abundant Nb species were able to interact with Co (II) species. When the dosages of EB and TBHP were 10 mmol and 30 mmol, respectively, the reaction temperature was 100 °C, and the reaction time was 10 h, the conversion rate of ethylbenzene was 62%, and the selectivity of AP was 84.7%.

Enhanced low-temperature activity and huimid-SO2 resistance of MnFe-based multi-oxide catalysts for the marine NH3-SCR reaction

Several MnFe-based multi-metal oxides were synthesized as NH3-SCR catalysts by a simple coprecipitation method for abating NOx of marine diesel exhausts. The Co and Nb-doped MnFeCeAl catalysts exhibit NOx conversion over 90% and N2 selectivity above 95% at 180–270 °C, especially the MnFeCeAlCo catalysts can inhibit nearly all sulfate species growth within 150 ppm humid-SO2 gases at 225 °C. The structural characterization results revealed that Co, Nb, Sm, and Sb doping can enhance interactions among different components and promote active component dispersion. Temperature programmed analysis indicated that the Co doping is not only more favorable for improving redox properties, but can also enhance the surface acidity, which are advantageous to improve the activity, N2 selectivity, and humid-SO2 resistance. Moreover, the XPS results implied that the binding energy shift or the valence variation of the Sm, Sb, Nb, and Co species on catalyst surfaces are favored to raise the atomic ratios of high-valent Mn species and surface adsorbed oxygen, which can promote the redox property significantly and further facilitate SCR activity. Accordingly, the excellent activity and humid-SO2 tolerance of the MnFeCeAlCo catalyst should attribute to its lower redox temperature, strong interaction between oxides, 47.3% surface Mn4+/Mn3+ species, and 71.8% adsorbed oxygen, which provide a method for improving the SCR performances of MnFe-based catalysts with humid SO2 resistance.

Bis(neopentylglycolato)diboron (B2nep2) as a bidentate ligand and a reducing agent for early transition metal chlorides giving MCl4(B2nep2) complexes.

We found that bis(neopentylglycolato)diboron (B2nep2) served as a bidentate ligand and a one-electron reducing agent for early transition metal chlorides to afford MCl4(B2nep2). Treatment of B2nep2 with MCl5 (M = Nb and Mo) produced MCl4(B2nep2) via two successive reactions, coordination of B2nep2 to the metal center and one-electron reduction from M(V) to M(IV), while coordination of B2nep2 to MCl4 (M = Zr, Ti) was observed without reduction of the central metals. DFT studies for the reduction of NbCl5 by B2nep2 clarified the initial formation of seven-coordinated and B2nep2-ligated Nb(V) species, NbCl5(B2nep2), and one chloride on niobium(V) moves to the Lewis acidic boron center to generate NbCl4[(B2nep2)Cl]. The chloride on the boron atom of NbCl4[(B2nep2)Cl] is trapped by the second B2nep2 to give [NbCl4(B2nep2)][ClB2nep2]. After the formation of [ClB2nep2]- as an anionic sp2-sp3 diboron adduct, one-electron reduction of the niobium(V) center produces NbCl4(B2nep2) along with [ClB2nep2]˙ as a plausible diboron species, whose decomposition affords ClBnep and B2nep2. The reduction of metal halides in the presence of B2nep2 was exemplified by green LED irradiation of TiCl4(B2nep2), producing chloride-bridged titanium(III) species, (B2nep2)TiCl2(μ-Cl)2TiCl2(B2nep2).

Catalytic one-pot conversion of biomass-derived furfural to ethyl levulinate over bifunctional Nb/Ni@OMC

As one of the important chemical feedstocks and biofuels, ethyl levulinate (EL) can be produced from biomass-derived furfural by consecutive hydrogenation, etherification and ring-opening reactions. However, this process normally requires two separate steps in different reaction systems, which is complex and energy consumption. Herein, Nb–Ni bifunctional ordered mesoporous carbons (Nb/Ni@OMCs) were synthesized by a two-step process where Ni@OMC was firstly synthesized by a solvent evaporation induced self-assembly (EISA) process using F127 as a template agent, polyphenol gallic acid as carbon precursor and Ni2+ as cross-linker, following with the supporting of Nb species in the Ni@OMC by an incipient wetness impregnation method. The as-synthesized Nb/Ni@OMC samples were applied for the one-pot catalytic transformation of furfural to EL, and exhibited good activity with the highest EL yield of 83% under an optimized condition. Two possible pathways for the one-pot production of EL were proposed according to two intermediates: (1) hydrogenation of furfural to form furfuryl alcohol (FFA) that is then etherified with ethanol to form 2-(ethoxymethyl)furan (2-EMF); and (2) acetalization and etherification of furfural with ethanol to produce 2-(diethoxymethyl)furan (2-DMF). Then both 2-DMF and 2-EMF are converted to EL through acid catalyzed ring opening reaction. The dominant reaction pathway varied with the properties of the catalyst and the applied reaction conditions.

The promoter effect of Nb species on the catalytic performance of Ir-based catalysts for VOCs total oxidation

Ir/TiO2 catalysts promoted by niobium have been synthesized, characterized by different complementary techniques, and tested for the total oxidation of a set of alkanes and their mixtures. The addition of appropriate amounts of niobium to Ir/TiO2 catalysts resulted in a remarkable increase in the catalytic activity compared to the Nb-free Ir/TiO2 catalysts. The promotion caused by the presence of niobium has been related to the massive presence of isolated IrOx surface species which, interestingly, present remarkable reducibility and, consequently, excellent catalytic activity. Conversely, the IrOx species formed in the catalyst in the absence of niobium also include IrO2 clusters with lower intrinsic reactivity. Similarly, Nb-loadings exceeding the theoretical monolayer tends to the formation of bulk Nb2O5 species on the titania surface that provokes the formation of IrO2 nanoclusters. A positive influence on the reactivity of non-stoichiometric surface Ti3+ species that generates oxygen vacancies is also observed.

Low‐Tortuous MXene (TiNbC) Accordion Arrays Enabled Fast Ion Diffusion and Charge Transfer in Dendrite‐Free Lithium Metal Anodes

AbstractThe widespread implementation of lithium metal anodes is indispensable for reviving high energy density lithium metal batteries. However, the sluggish ion diffusion and high charge‐transfer resistance in metallic lithium anodes hamper their rate capability and practical applications. Here, low tortuous MXene arrays are developed through the ultrafast spreading of an aqueous accordion‐like TiNbC‐MXene dispersion onto a hydrophobic surface. The low tortuous MXene arrays facilitate the fast infiltration of electrolytes, enabling the rapid diffusion of lithium ions. The MXene arrays with Nb species significantly improve the charge transfer in the electrode, homogenizing the electric field. Thus, the low tortuous MXene arrays constructed electrode without lithium dendrites delivers a high‐rate capability (20 mA cm−2) with a long cycle life (2500 cycles). Full cells with the dendrite, low tortuosity MXene arrays as anode show a high rate cycle stability up to 1000 cycles (4 C) under conditions of low negative/positive capacity ratio (2.0).

The effect of different atmosphere treatments on the performance of Ni/Nb–Al2O3 catalysts for methane steam reforming

Methane steam reforming is currently the most widely used hydrogen production reaction in industry today. Ni/Nb–Al2O3 catalysts were prepared by treatment under H2, N2, and air atmosphere prior to reduction and applied for methane steam reforming reaction at low temperature (400–600 °C). The hydrogen-treated catalysts increased catalytic activity, with 55.74% methane conversion at S/C = 2, GSVH of 14400 mL g−1 h−1 and 550 °C. The H2 atmosphere treatment enhanced the Ni–Nb interaction and the formation of stable, tiny, homogeneous Ni particles (6 nm), contributing to good activity and stability. In contrast, the catalysts treated with nitrogen and air showed weaker interactions between Ni and Nb species, whereas the added Nb covered the active sites, which caused the decrease in activity. Meanwhile, carbon accumulation was also observed. This work is informative for preserving small nano-sized nickel particles to enhance catalytic performance.

Hierarchically MOx@Nb-zeolites for the selective oxidation of HMF to HMFCA

The oxidation of 5-hydroxymethylfurfural (HMF) to 5-hydroxymethyl-2-furancarboxylic acid (HMFCA) has been investigated on MOx@Nb-zeolite catalytic systems (where MOx = CoOx, MnOx or FeOx and zeolite - USY and Beta) with hierarchical texture and acid-base properties. These catalysts were exhaustively characterized by several techniques such as XRD, adsorption-desorption of liquid nitrogen at 77 K, CO2- and NH3-TPD, DRIFT, XPS, and SS NMR. The new hierarchically catalysts produced HMFCA with a selectivity of 97.0% for a XHMF = 95.0% (Mn@Nb-Y30). A synergetic effect between MOx and Nb species in the activation of t-BuOOH and oxidation of HMF has been identified. The absence of FDCA in the reaction products using MOx@Nb-zeolite catalysts can be due to the preponderant presence of the acidic sites (associated to both framework and extra framework AlOx) which prevent a further oxidation of HMFCA to FDCA.